1. Field of the Invention
The invention concerns a procedure for dewatering of sewage sludge, whereby the pumpable sludge and the sludge made pumpable by breaking up solid substances is subjected to chemical pretreatment with addition of flocculation agents; thereafter the sludge is dewatered to form a sludge cake by pressing; said sludge cake is then destined for further utilization or final storage.
The procedure according to the present invention is also directed to raw sludges and digested sludges of local sewage purification plants as well as to industrial sewages.
2. Description of the Prior Art
The present invention starts from the process for dewatering of sewage sludge as described in DE-OS 28 38 899 in which the crumbled and chemically pretreated sludge is directly led to an extractor press, in which it is conveyed by a screw from the bottom to the top, with other words: in which the sludge is pumped up. A chemical pretreatment of the sludge, particularly with flocculants, however, is impaired in its effect if the sludge cake treated in this manner is exposed to pumpage.
On principle, the main aim of the previously described sludge dewatering procedure is to reduce as far as possible the volume of the sludge to economize the volume of deposit as well as the transport and depositing costs and to give the sludge the highest possible shearing resistance in order to guarantee a long time of depositing capability. The best dehydrating units, i.e. the chamber filter presses, actually reach only 32-35% of (dry substance at maximum). It results a relatively high remaining humidity which causes many problems for the depositing capability. Therefore, the development tends to burn the sewage sludge with addition of primary energy, i.e. to destroy the sludge.
However, the sewage sludge is a precious substance and it should not simply be thrown away on dumping places or destroyed, and this with the addition of primary energy.